1. Field of the Invention
This invention relates to medical devices, and more particularly to implantable cardioverter defibrillators (ICD) used to cardiovert and/or defibrillate a human being. The ICD pulse generator kite-tail electrode system of this invention improves the performance of ICDs.
2. Background Information
The implantable cardioverter defibrillator is a well established therapy for malignant ventricular arrhythmia. The ICD senses an arrhythmia, stores a charge in an internal capacitor, and delivers that charge to the heart through electrodes.
An early form of electrodes are epicardial or pericardial patches which are sewn to the surface of the heart. Electrodes of this type are shown in FIG. 1. Epicardial or pericardial patch electrodes are disclosed in U.S. Pat. No. 4,821,723 to Baker, Jr. et al. and U.S. Pat. No. 4,827,932 to Ideker, et al. Another well know form of electrodes are endocardial lead electrodes which traverse the patient's vasculature and are disposed within the heart, preferably the right ventricle. A hybrid system uses endocardial leads in conjunction with epicardial patches. This system is disclosed in U.S. Pat. No. 4,548,203 to Tacker, Jr. et al. and U.S. Pat. No. 4,641,656 to Smits.
Most electrode systems which utilize epicardial patches require open chest surgery for implantation and positioning. Such surgery is traumatic, risky, expensive and requires a long patient recovery period. Referring to FIG. 2, procedures were therefore developed to subcutaneously implant a patch electrode in the left side of the patents chest or in the back under the shoulder blade. U.S. Pat. No. 4,662,377 to Hileman et al. teaches such a method. U.S. Pat. No. 4,727,877 to Kallock and U.S. Pat. No. 5,014,696 to Mehra disclose a similar method wherein a rigid plate is used in place of a patch. The advantage of these subcutaneous implantation methods is that major surgery is avoided, while at the same time improved performance is provided by the combination of the large surface area electrode element with the endocardial lead electrode.
Another approach used is to pericardially implant an electrode. In such systems, an electrode is implanted near the epicardial surface of the heart via an insertion through a small incision or an introducer apparatus. The electrodes simulate the epicardial electrodes, but avoid the trauma of open chest surgery. Pericardial electrodes and methods are disclosed in U.S. Pat. No. 4,860,769 to Fogarty et al. and U.S. Pat. No. 4,991,578 to Cohen.
Referring to FIG. 3, a recent development in ICD electrodes is the "pitchfork electrode" disclosed in U.S. Pat. No. 5,203,348 to Dahl, et al. This approach replaces the large surface area of the subcutaneous patch style electrode comprising three parallel wires forced about the patient's left side. Although the surface area of the electrodes is not great, the convex hull "outline" or "shadow" formed by the wires is large. This technique results in a very low impedance and also low defibrillation energy thresholds. Unfortunately, the implantation technique is complex and time consuming. Also, the low impedance is not consistent with the modem trend toward smaller ICD capacitance's which show the most benefit with high impedance.
Referring to FIG. 4, another recent electrode system approach is to use the housing or can of the ICD pulse generator as an electrode in conjunction with an endocardial lead electrode. This technique is shown in published European Patent Application 0453761A1 and in U.S. Pat. No. 5,133,353 to Hauser, U.S. Pat. No. 5,261,400 to Bardy and in U.S. Pat. No. 5,376,103 to Anderson. This approach, although it has advantages, is inconsistent with another trend in ICD design, namely that toward smaller ICD housing. Smaller housings will reduce the effective size of the electrode formed thereby, which will yield reduced performance. Anderson teaches the use of a subcutaneous electrode in conjunction with the ICD housing electrode, but this technique requires the addition of an external connection to the housing and the attendant complication of connectors, feedthrus, and cables, as well as the resultant increase in size of the housing, to accommodate the connector and feedthru.
Despite the need in the art for a safe, easy to implant, effective, and reliable electrode system for use with an ICD, and which overcomes the disadvantages, shortcomings and limitations of the prior art, none insofar as is known has been developed or proposed.
Accordingly, it is an object of the present invention to provide a new electrode system for use with an ICD. It is a further object of this invention to provide an electrode system which is safe, easy to implant, reliable and effective, and which overcomes the limitations and shortcomings of the prior art.